Wood Bioenergy Carbon Accounting –
Beyond Carbon Neutrality
2011 National FIA User Group Meeting
Sacramento, CA
March 8-10, 2011
Ken Skog, Project Leader
USDA Forest Service
Forest Products Laboratory
Madison, Wisconsin
Topics
 What are the “right” or “helpful” research questions to ask
about wood bioenergy carbon emission offsets?
 A Joanneum Research study – GHG offsets by wood
source over time
– Carbon neutrality number over time – CN(t)
• Logging residue [temperate forests]
• Intensified thinnings [Austria]
• Intensively managed forest plantations
– on fallow ag land
– by clearing existing forest (if time)
 More forestry research questions
Possible “right” or “helpful” questions
(my translation of sources)
 Searchinger et al. – to what degree does an increase wood energy
use decrease GHG emissions [over time] by alteration of forest
growth/ emissions.
 6/18/2010 letter from Forestry groups to EPA Administrator – Is an
increase in wood energy use “good” as long as forests are
managed sustainably and forest carbon is increasing? (letter says
yes) Good? = less carbon emissions “overall” to the atmosphere?
 Manomet study – How quickly (years) and by how much will
emissions from fossil fuel power system be offset by increasing
use of Mass. forest biomass in selected wood-power systems?
 Joannuem Research – By increasing use of a specific source of
wood fuel use in place of fossil fuel for power, what fraction of a
fossil systems emissions would be offset by using specific wood
sources in t years?
Question: By increasing use of a
specific source of wood fuel use in
place of fossil fuel for power,
what fraction of a fossil power
emissions would be offset by using
specific wood sources in t years?
Bioenergy
system
Fossil fuel
system
Source: Giuliana Zanchi
Setting up the problem - 1
 Focus:
– What is the emission offset of an increase in
wood use ( to a new constant level) to make
electric power/ heat and power
 Assume
– kwh / kg wood carbon = kwh / kg of coal carbon
– Kwh / kg natural gas carbon = 0.6 kwh / kg wood
carbon
 Exclude emissions to obtain and transport wood or
fossil fuel
Setting up the problem - 2
 Compute carbon neutrality number, CN(t)
– Fraction of fossil emissions offset by time t
by increase in wood use from a given source
CN (t) = [EFF(t) – NEw(t)] / EFF(t)
EFF(t) = Cumulative fossil fuel emissions avoided
NEw(t) = Cumulative wood emissions to time t –
Change in forest growth/ emissions due wood energy
use to time t
CN(t) < 1 cumulative net wood emissions > than fossil emissions
CN(t) = 0 cumulative net wood emissions = fossil emissions
CN(t) = 1 net wood carbon storage totally offsets fossil emissions
Examples: CN(t) for wood use from
1. Additional harvest from a managed forest
2. Logging residues from a managed forest
3. New plantations on fallow land
4. New plantation after harvesting existing forest
Illustrative case studies
 Model: GORCAM (Graz Oak Ridge Carbon Accounting Model)
 Growth curve based on Austrian yield table for Spruce
 No disturbances included
35
1.5
1.0
15
0.5
5
-5 0
50
100 150
0.0
200 250 300 350 400
CN
Emissions (Gg CO2)
25
• Biomass net emissions
(green)
• Fossil fuel emissions
(orange)
• CN factor (black)
-0.5
-15
Biomass
Fossil Fuel
-25
-1.0
CN
-35
-1.5
Year
Source: G. Zanchi
1. Additional fellings from a managed forest (1)
Rotation period: 90 years
Rotation forest: 90 hectares
Harvesting:
a) Baseline: 60% of increment
b) New Management: 80% of increment
The additional biomass is used for bioenergy
C stock
50
1000 tC
40
30
20
Bioenergy system
10
Fossil fuel system
(baseline)
0
-270
-180
-90
0
90
Year
180
270
360
Source: G. Zanchi
1. Additional fellings from a managed forest (2)
Rotation period: 90 years
Rotation forest: 90 hectares
Harvesting:
a) Baseline: 60% of increment
b) New Management: 80% of increment
The additional biomass is used for bioenergy
35
1.5
1.0
15
0.5
5
-5 0
50
100 150
0.0
200 250 300 350 400
-0.5
-15
Biomass
Fossil Fuel
-25
-1.0
CN
Emissions (Gg CO2)
25
• Biomass net emissions
(green)
• Fossil fuel emissions
(orange)
• CN factor (black)
• CN(t) = 0 at ~ t = 180 yrs
• CN(400) = ~ 0.5
CN
-35
-1.5
Year
Source: G. Zanchi
2. Felling residues from a managed forest
30
1.5
20
1.0
10
0.5
0
0.0
400
0
50
100
150
200
250
300
350
-10
• Biomass net emissions
(green)
• Fossil fuel emissions
(orange)
• CN factor (black)
CN
Emissions (Gg CO2)
• Rotation period: 90 years (90 ha)
• Baseline: Logging residue left in the forest
• New Management: 2/3 logging residue to bioenergy
For a coal alternative
CN(30) = 0.6
-0.5
Biomass
Fossil Fuel
-20
-1.0
If natural gas is the alternative
CN(30 ) = 0.3
CN
-30
-1.5
Year
Source: G. Zanchi
3. New plantations
• Baseline: low carbon change land (e.g. cropland)
• New Management: new forest to produce bioenergy (no forest land
use change)
100
100.0
75
10.0
25
0
0
100
200
300
1.0
400
-25
-50
-75
Fossil Fuel
Biomass
CN
CN
Emissions (Gg CO2)
50
• Biomass net emissions
(green)
• Fossil fuel emissions
(orange)
• CN factor (black)
0.1
• CN(t) >1 for all t
-100
0.0
Year
Source: G. Zanchi
Forestry research questions for the U.S.
on wood energy carbon offsets
 For logging residue – what is CN(t) by location? (generate
U.S. map using logging residue decay curves)
 Are there better metrics of emission offset over time ? (e.g.
relative cumulative radiative forcing – wood vs fossil fuel)
 CN(t) for current timber management with more thinnings,
by forest type
 CN(t) for fire hazard reduction thinnings?
 CN(t) for mill residue (is landfill the alternate decay if not
used? Composite products? pulp?)
 Are there broad management guidelines for thinnings to
attain say CN(100) > 0.5? (e.g. Marland and Marland
1992)
Publications
Manomet study: Walker, T. (Ed.). Contributors: Cardellichio, P., Colnes, A., Gunn, J., Kittler, B.,
Perschel, R., Recchia, C., Saah, D., and Walker, T. 2010. Biomass Sustainability and Carbon
Policy Study: Report to the Commonwealth of Massachusetts Department of Energy
Resources. Manomet Center for Conservation Sciences. Report No.: NCI-2010-03.
Repo A., Tuomi M., Liski J., 2010. Indirect carbon dioxide emissions from producing bioenergy
from forest harvest residues. GCB Bioenergy, no. doi: 10.1111/j.1757-1707.2010.01065.x
McKechnie J., Colombo S., Cheng J., Mabee W., MacLean H.L. Forest bioenergy or forest
carbon? Assessing trade-offs in greenhouse gas mitigation with wood-based fuels. Environ Sci
Technol. 2011 Jan 15;45(2):789-95
Palosuo T, Wihersaaari M, Liski J, 2001. Net Greenhouse Gas Emissions due to energy use of
forest residues –Impacts of soil carbon balance. Woody biomass as an energy source –
Challenges in Europe. EFI proceedings no 39, 2001
Schlamadinger B and Spitzer J, 1994. CO2 mitigation through bioenergy from forestry
substituting fossil energy. In: Biomass for energy, environment, agriculture and industry.
Proceedings of the 8th European Biomass Conference.Vienna, Austria, 3-5 October 1994,
Volume 1. Ed. Chartier P., Beenackers A.A.C.M., Grassi G., pp. 310-321.
Schlamadinger B, Spitzer J, Kohlmaier GH, Lüdeke M, 1995. Carbon balance of bioenergy from
logging residues. Bioamss and Bioenery 8 (4): 221-234.
Schlamadinger B and Marland G, 1996. The role of forest and bioenergy strategies in the global
carbon cycle. Biomass and Bioenergy 10 (5/6): 275-300.
Source: G. Zanchi
Thank you
Ken Skog – kskog@fs.fed.us
4. New plantations – existing forest is converted
• Baseline: Existing forest is converted
• New Management: new forest to produce bioenergy
• Biomass net
emissions (green)
• Fossil fuel emissions
(orange)
• CN factor (red)
• CN(t) < 0 for t < ~80
years
Source: G. Zanchi